Ron Guth: One variety of the 1856-S Eagle features a mintmark placed beneath the talon and the fletch of the arrow. While this is an unusual positioning for an S-Mint No Motto Eagle, it is normal for most other mintmarked No Motto Eagles. All this indicates is that Mint employers were not always consistent in their placement of mintmarks, which were added by hand to the individual dies.
David Akers (1975/88): The 1856-S is rare in any condition and is particularly rare in high grade. Only a few that grade as high as AU are known and there are no more than two or possibly three uncirculated examples. When available, this date is invariably only VF or EF. It is interesting to note that despite its considerable rarity, the 1856-S is the second commonest S-Mint Eagle (the 1854-S is the most common) prior to 1879. This is a strong indication of just how rare these San Francisco Mint issues are because the 1856-S is by no stretch of the imagination common. Both small and large mintmark varieties exist and the Small S variety is the more common.
Ellen D Collection (PCGS Set Registry) - Simpson Collection